1. Field of the Invention
The invention relates to a method for dicing apart semiconductor devices formed together upon a single underlying heat sink or other metal layer.
2. Description of the Prior Art
Prior to the present invention, knife-blade slicing and laser scribing were the two most widely used techniques for dicing apart semiconductor device mesas formed upon a single underlying heat sink. Both of these suffered from a number of disadvantages. With knife-blade slicing, stress transmitted to the mesa through the heat sink being cut often caused severe degradation in the I-V characteristics of the diode. Deformation of the heat sink also made effective bonding of the semiconductor chip to a second header difficult. Mesas could be broken or chipped due to the stresses produced. Knife-blade slicing was also slow requiring four individual knife cuts per mesa. The effective mesa yield per wafer was reduced since a lower limit had to be put upon the mesa spacing due to the width of the slicing blade. Also, only rectilinear shapes could be produced using knife-blade slicing. Although in many applications circular or other non-rectilinear shapes were desirable to obtain optimum heat flow characteristics, such shapes could not be produced.
With laser scribing, the diodes or other semiconductor devices were subjected often to excessive heating and could be damaged by poorly focussed laser beams or flying debris. Clean-up following the scribing operation was difficult due to burned-on wax and photoresist. As in the case of knife-blade slicing, a practical lower limit to the separation of the mesas was imposed due to limitations in laser beam guidance and focussing. Laser scribing also required complex, expensive and sometimes hazardous equipment. This process was also time consuming, although perhaps not so much as knife-blade slicing. Moreover, laser scribing, as knife-blade slicing, was limited to producing rectilinear shapes.